On Fri, Jun 05, 1998 at 03:10:10PM -0400, Barry Cooper wrote:
>   I keep running across references to 2's complements, does anyone have a
> relatively simple explanation?

A 2's complement is a variation on 1's complement; the 1's complement of
a binary number is just the number with all bits inverted, e.g.

01101010

has a 1's complement of

10010101

where each bit is individually toggled.

Now a 2's complement is a 1's complement plus 1, so the 2's complement of the
first number is

10010110

Note that a 1 value has been added to the number (causing overflow into the
second bit).

The value of 2's complement derives from the fact that the 2's complement of zer
o
is also zero (try it out, ignore the overflow from the high order bit).
This makes it a good operation to use for negating a binary number, and is the
representation used by 99.9% of all computer architectures for representing sign
ed
numbers (where negative zero equals zero).

--
Clyde Smith-Stubbs               |            HI-TECH Software
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